Edit: I didn’t understand how a jet engine worked, but now that I do, the question has been amended to this…
“Why does a rocket have to travel faster and faster the higher up it goes? Shouldn’t it require less and less speed as it is further from the earth it gets because there is a non-zero number(very small) of negative gravity change the higher you are?”
Edit #2: I think I suck at asking this so I’ll ask it like a 5 year old.
We have all seen videos of rockets taking off. They start very slowly, and then build in speed. Although, at first, they build up in speed. It’s not as if they torque off the earth at 20,000mph, although that would be ASTOUNDING to see. So here’s my super drawn out really dumb question that I cannot wrap my head around the answer for the life of me.
Let’s say you have a rocket going 100mph going 90 degrees straight up from the surface of the earth. Why can’t it just keep going 100mph straight up. Just keep going and going. Up, straight up. Up up up and away? Why can it move up starting from zero miles an hour? If it can move up at 5mph even for an instant, why can’t it continue at that velocity all the way up.
All the answers have been wonderful if I was asking how to get something in orbit. I’m asking why 100mph 90 degrees going straight up works down here, but not up there? I cannot find a straight answer to this question no matter what I google. I appear to be bad at research or this is just a stupid ass question. I really just don’t understand the physics of this at all.
Let’s try this another way. Say I threw a magic baseball that whatever velocity it was tossed at, it maintained until it hit a object. It doesn’t disregard gravity. It just has a magic anaerobic motor that maintains the speed. Like cruise control. Say I throw it 90 degrees straight up at 35mph. Will it leave Earth? Why or why not?
In: Engineering
>Let’s say you have a rocket going 100mph going 90 degrees straight up from the surface of the earth. Why can’t it just keep going 100mph straight up. Just keep going and going. Up, straight up. Up up up and away? Why can it move up starting from zero miles an hour? If it can move up at 5mph even for an instant, why can’t it continue at that velocity all the way up.
At the altitude of the international space station, gravity is still 90% as strong as it is on the ground, so you have to be going sideways fast enough that the planet curves away as fast as you fall down. That’s why you have to go super fast to get into orbit. You only go up first in order to get out of the atmosphere so it doesn’t burn you up and slow you down.
Once you’re in orbit, going faster in the same direction you’re moving will make the other side of your orbit go higher, because you’re adding energy for the distance you travel in the direction of the force applied. If you try to burn straight up while in orbit, your orbit will go higher 1/4 orbit in front of you, but it will go lower 1/4 orbit behind you.
As for gravity getting weaker as you go higher, that’s true, but you still need more energy to get that high than you do to go 17,000mph in low orbit.
Atmosphere aside, if you threw a ball straight up at escape velocity, it wouldn’t fall back down, but that’s more like 25,000mph.
As for the magic baseball, that depends on its exhaust velocity, it would have to be absurdly high in order to overcome the gravity losses for moving so slow.
Basically, if you’re hovering, 100% of the fuel you burn is wasted, 0% of it is helping you get where you’re going. holding a constant 35mph is very very close to just hovering. Even with the most efficient chemical rockets on the planet you’d be out of fuel in 10 minutes at that level of thrust, having only gone up 5~6 miles. The farther you move in the direction of thrust, the more energy you get out of that burn, so you want to be going as fast as possible as early as you can. For more information on this, search for “Oberth effect”.
I strongly recommend you play the game Kerbal Space Program.
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